Mothods for processing a coating film and for manufacturing a semiconductor element

ABSTRACT

According to the present invention, there is provided a method for processing a coating film, including the steps of forming a silica group coating film having a low dielectric constant on a substrate, etching the silica group coating film through a resist pattern, and processing the silica group coating film with plasma induced from a substantially inactive gas such as helium gas or the like. In this method, the silica group coating film is not damaged when an ashing process is conducted to the resist pattern as a subsequent process, and the low dielectric constant can be maintained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for processing a silicagroup coating film having a low dielectric constant used in a copperdamascene method, and more specifically to a method for processing asilica group coating film having a dielectric constant equal to or lessthan 3.2 in the formation of a multi-layer wiring structure, using acopper damascene.

[0003] 2. Description of Prior Art

[0004] The need for high integration of semiconductor devices isincreasingly rising, and now we are running into a generation of 0.13 μmgate lengths. It is already recognized that, by using Cu as a wiringmaterial in such instances in place of the conventional Al, thecharacteristics of manufactured semiconductor elements can be improvedin the following aspects.

[0005] Cu is superior to Al in tolerance for EM (i.e.,electromigration). Also, Cu has low resistance, and thereby it ispossible to reduce signal delay due to wiring resistance. The use underhigh current density can be achieved, that is, an allowable currentdensity can be improved by three (3) times or more, and thereby thewidth of wiring can be made fine.

[0006] However, since it is difficult to control the etching rate of Cucompared to Al, a copper damascene method attracts attention as a methodfor realizing multi-layer wiring of Cu without any etching process. Alot of proposals have been made (for example, Japanese unexamined patentapplication publication No. 2000-174023 and Japanese unexamined patentapplication publication No. 2000-174121).

[0007] Explanation of the copper damascene method will now be given withreference to FIG. 5.

[0008] First, as shown in FIG. 5(a), an intermediate insulating film,which is comprised of SiO₂ through a CVD method or SOG and has a lowdielectric constant, is formed on a substrate, and a resist mask havinga pattern is provided thereon. By etching, as shown in FIG. 5(b), wiringgutters are formed. Next, as shown in FIG. 5(c), the wiring gutters arelined with barrier metal, and as shown in FIG. 5(d), Cu is embedded intothe gutters by means of electrolysis plating so as to form a lower layerwiring. After polishing the barrier metal and Cu by chemical polishing,as shown in FIG. 5(e), another intermediate insulating film is formedthereon. In the same manner, by selectively etching the intermediateinsulating film through a resist mask having a pattern, as shown in FIG.5(f), via-holes (or contact holes) and trench holes (i.e., gutters foran upper layer wiring) are formed (dual damascene). As shown in FIG.5(g), the via-holes and the gutters for an upper layer wiring are linedwith barrier metal, as shown in FIG. 5(h), Cu is embedded into thevia-holes and the gutters for an upper layer wiring by means ofelectrolysis plating or the like, and thereby an upper layer wiring isformed.

[0009] In the above-mentioned explanation, copper is used for formingwiring in a damascene method. However, a damascene method can beconducted with aluminum. The present invention can be applied to adamascene method using various conductive metal as well as the copperdamascene method.

[0010] When multi-layer wiring is formed by a damascene method, it isrequired that an aspect ratio (i.e., height/width) of via-holes shouldbe increased for micros. However, if SiO₂ through a CVD method is usedfor an intermediate insulating film, the aspect ratio will be at most 2.Also, the dielectric constant of SiO₂ is relatively high (ε=4.1), whichis not satisfactory.

[0011] Therefore, the use of organic or inorganic SOG having a lowerdielectric constant has been examined. Further, it is desired to makethe dielectric constant of organic or inorganic SOG lower.

[0012] It is recognized that the dielectric constant of an intermediateinsulating film can be decreased by making the intermediate insulatingfilm porous. However, the lower dielectric constant of the intermediateinsulating film decreases the density of the film. As a result of this,damage or crack occurs in the intermediate insulating film when a plasmaashing process of a resist film is conducted as a subsequent process,and thereby it is difficult to obtain a reliable semiconductor element.

[0013] It is supposed that the reason of the damage in the intermediateinsulating film is because Si—R group (R means lower alkyl group orhydrogen atom) is decomposed (R group is separated) by the ashingprocess and Si—OH bond is produced.

[0014] For example, in the case of organic SOG, Si—CH3 bond (CH3 is anexample) is broken to be Si—OH. In the case of inorganic SOG, Si—H bondis broken to be Si—OH.

SUMMARY OF THE INVENTION

[0015] According to the present invention, to solve the problems asmentioned above, there is provided a method for processing a coatingfilm comprising the steps of forming a silica group coating film havinga dielectric constant equal to or less than 3.2 (preferably equal to orless than 2.7) on a substrate, etching the silica group coating filmthrough a resist pattern, processing the silica group coating film, towhich an etching process has been conducted, with plasma induced frominactive gas such as helium gas or the like, and removing the resistpattern by an ashing process.

[0016] It is possible to prevent damage in an ashing process byconducting a pre-ashing process with plasma induced from inactive gassuch as helium gas or the like. It is supposed that the reason isbecause plasma induced from inactive gas such as helium gas or the likeattacks the coating film having Si—H group and Si—H bond in the surfacelayer is changed into Si—O—Si bond.

[0017] The dielectric constant equal to or less than 3.2 is required foran intermediate insulating film used in a damascene method. A lowerdielectric constant is preferred. The silica group coating film is notlimited to a particular one as far as it has such a dielectric constant.The silica group coating film having such a dielectric constant can beachieved by forming with coating liquid as follows:

[0018] The coating liquid can include a condensation product which isobtained through hydrolysis of trialkoxysilane within an organic solventunder an acid catalysis. In particular, it is preferable to obtain thecoating liquid by dissolving trialkoxysilane having a concentration of1-5 weight % in a case of converting into SiO₂ into alkylene glycoldialkyl ether, adding water of 2.5-3.0 mols per 1 mol of thetrialkoxysilane to this solution and adjusting the content of alcoholproduced through a reaction in a reacting mixture to be less than orequal to 15 weight % after conducting a hydrolytic condensation under anacid catalyst.

[0019] An intermediate insulating film having a ladder structure can beobtained by using trialkoxysilane having a concentration of 1-5 weight %in a case of converting into SiO₂. Independent of being organic orinorganic, by making a ladder structure, a film which is dense and has alow dielectric constant can preferably be formed as mentioned above.

[0020] As the above-mentioned trialkoxysilane, it is possible to listtrimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane,diethoxy monomethoxysilane, monomethoxy dipropoxysilane, dibutoxymonomethoxysilane, ethoxy methoxy propoxysilane, monoethoxydimethoxysilane, monoethoxy dipropoxysilane, butoxy ethoxypropoxysilane, dimethoxy monopropoxysilane, diethoxy monopropoxysilane,and monobutoxy dimethoxysilane. Among these, compounds preferable inpractice are: trimethoxysilane, triethoxysilane, tripropoxysilane, andtributoxysilane. In particular, trimethoxysilane and triethoxysilane arepreferable.

[0021] As the solvent, in order to increase the stability ofpreservation, it is necessary to use alkylene glycol dialkyl ether. Byusing this, it is possible to control a decomposition reaction of H—Sigroup in trialkoxysilane or a substitution reaction of hydroxy group foralkoxy group in silanol produced as an intermediate product, whichoccurs in the conventional art using lower alcohol as a solvent, andthereby it is possible to prevent the gelation.

[0022] As the alkylene glycol dialkyl ether, it is possible to list adialkylether type of alkylene glycol such as ethylene glycoldimethylether, ethylene glycol diethylether, ethylene glycoldipropylether, ethylene glycol dibutylether, diethylene glycoldimethylether, diethylene glycol diethylether, diethylene glycoldipropylether, diethylene glycol dibutylether, propylene glycoldimethylether, propylene glycol diethylether, propylene glycoldipropylether, and propylene glycol dibutylether. Among these, apreferable compound is a dialkylether type, in particular, adimethylether type of ethylene glycol or propylene glycol. These organicsolvents may be used alone or by combining two or more kinds thereof.Also, these organic solvents are used at a ratio of 10-30 times mol withrespect to 1 mol of alkoxysilane.

[0023] It is necessary that water used for hydrolysis of trialkoxysilanebe within a range of 2.5-3.0 mols with respect to 1 mol oftrialkoxysilane, preferably within a range of 2.8-3.0 mols, so as toincrease the degree of hydrolysis. If it is too small compared to thisrange, although the stability in preservation is increased, the degreeof hydrolysis is deteriorated, the content of organic group in thehydrolysis product is increased, and thereby gas is generated at thetime of forming a coating film. If it is too much compared to thisrange, the stability in preservation is deteriorated.

[0024] Even if at least one kind of alkylene glycol dialkyl ether isused as a solvent rather than alcohol, since alcohol corresponding toalkoxy group is inevitably generated in the course of hydrolysis ofalkoxysilane, it is necessary to remove the generated alcohol from thereaction system. Specifically, it is necessary to remove the alcohol tobe less than or equal to 15 weight %, preferably to be less than orequal to 8 weight %, in the coating liquid. If the alcohol exceeds 15weight %, H—Si group and the generated alcohol react each other, RO—Sigroup is generated and the crack limit is deteriorated. In addition, gasis generated at the time of forming a coating film and theabove-mentioned trouble is caused.

[0025] As a method for removing the alcohol, it is preferable to conductdistillation under reduced pressure for 2-6 hours in a temperature of20-50° C. in a degree of vacuum of 30-300 mmHg, preferably 50-200 mmHg.The coating liquid obtained in this manner has characteristics ofshowing the increase in the weight of the film-forming component afterthe removal of the solvent in a thermogravimetric analysis, and nothaving its peak at 3,000 cm⁻¹ in the infrared absorption spectrum. Theconventional coating liquid, which is described in Japanese unexaminedpatent application publication No. Hei 4-216827 (1992), shows thedecrease in the weight in a thermogravimetric analysis, and has its peakin the vicinity of 3,000 cm⁻¹ in the infrared absorption spectrum, whichindicates that alkoxy group still exists therein.

[0026] One kind selected from polyalkylene glycol and the end alkylationproduct thereof may be included in the coating liquid. As a result ofthis, an intermediate insulating film can be made porous and thedielectric constant can be decreased.

[0027] As the polyalkylene glycol, it is possible to list lowerpolyalkylene glycol such as polyethylene glycol, polypropylene glycol orthe like. The end alkylation product means lower polyalkylene glycol inwhich hydroxy group in one or both end(s) of the lower polyalkyleneglycol is made to be alkoxyl with lower alkyl group such as methylgroup, ethyl group, propyl group, or the like.

[0028] The addition amount of the one kind selected from polyalkyleneglycol and the end alkylation product is 10-500 weight %, preferably50-200 weight %, with respect to the solid component of the coatingliquid.

[0029] The weight-average molecular weight of the polyalkylene glycoland the end alkylation product is 100-10,000, preferably 200-5,000. Thisrange can easily make the dielectric constant lower without any damageto solubility in the coating liquid.

[0030] According to the present invention, there is also provided amethod for manufacturing a semiconductor element comprising thefollowing steps of:

[0031] (1) forming a silica group coating film having a dielectricconstant equal to or less than 3.2 (preferably equal to or less than2.7) on a substrate;

[0032] (2) providing a resist pattern on the silica group coating film;

[0033] (3) etching the silica group coating film using the resistpattern as a mask;

[0034] (4) processing the silica group coating film with plasma inducedfrom inactive gas such as helium gas or the like; and

[0035] (5) conducting an ashing process to the resist pattern withplasma induced from oxygen gas.

[0036] In the above-mentioned step of forming a silica group coatingfilm, for example, coating liquid is applied onto a substrate such as asemiconductor substrate, a glass substrate, a metal plate, a ceramicsubstrate, or the like by means of a spinner method, a roll coatermethod, an immersion coating method, a spray method, a screen printingmethod, a brush painting method, or the like. It is dried to evaporatethe solvent therein and a coating film is formed.

[0037] In the steps of (2), (3) and (5), the conventional means can beused.

[0038] In the step of processing the silica group coating film withplasma induced from inactive gas such as helium gas or the like, aplasma processing apparatus for generating plasma gas from theabove-mentioned gas (for example, TCA-7822 manufactured by Tokyo OhkaKogyo Co., Ltd.) is used. The plasma processing is conducted underpressure of 10-600 mTorr, preferably 100-500 mTorr, and for 30-300seconds, preferably 30-120 seconds.

[0039] Another plasma processing apparatus may be used as well asTCA-7822. Also, as the inactive gas, neon, argon or the like may be usedas well as helium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a graph showing the infrared absorption spectrum of acoating film formed in embodiment 1 of the present invention after theashing process of the resist on the coating film;

[0041]FIG. 2 is a graph showing the infrared absorption spectrum of acoating film formed in embodiment 2 of the present invention after theashing process of the resist on the coating film;

[0042]FIG. 3 is a graph showing the infrared absorption spectrum of acoating film formed in comparative example 1 after the ashing process ofthe resist on the coating film;

[0043]FIG. 4 is a graph showing the infrared absorption spectrum of acoating film formed in comparative example 2 after the ashing process ofthe resist on the coating film; and

[0044]FIG. 5(a)-(h) show the steps of forming a multi-layer wiringstructure using a copper damascene.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] Hereinafter, embodiments according to the present invention willbe fully explained with reference to the attached drawings.

[0046] (Preparation of Coating Liquid)

[0047] Coating Liquid 1

[0048] Triethoxysilane of 73.9 g (0.45 mol) having a concentration of 3weight % in a case of converting into SiO₂ is dissolved and stirred intoethylene glycol dimethylether of 799.0 g (8.87 mol), a mixture of purewater of 24.2 g (1.34 mol) and nitric acid of 5 ppm is slowly stirredand dropped thereinto, and it is stirred for about 3 hours. Thereafter,it is left still for 6 days in a room temperature, so as to obtain asolution.

[0049] Reduced-pressure distillation is conducted to this solution at120-140 mmHg and 40° C. for 1 hour, and coating liquid is prepared. Inthe coating liquid, the concentration of solid component is 8 weight %and the concentration of ethanol is 3 weight %. This solution is coatingliquid 1.

[0050] The dielectric constant of a coating film formed with coatingliquid 1 is 3.1.

[0051] Coating Liquid 2

[0052] A both-end methylation product of polyethylene glycol havingweight-average molecular weight of 200 is added to coating liquid 1 at aratio of 100 weight % to the solid component of coating liquid 1,sufficiently stirred and thereby a uniform solution is obtained. Thissolution is coating liquid 2.

[0053] The dielectric constant of a coating film formed with coatingliquid 2 is 2.6.

[0054] (Embodiment 1: Coating Liquid 1 and He Processing)

[0055] A substrate is rotated and coated with coating liquid 1, andthereby a coating film having a thickness of 4500 Å is formed on thesubstrate. The refractive index of the coating film is 1.40.

[0056] A resist pattern is formed on the coating film. An etchingprocess is conducted using the resist pattern as a mask and wiringgutters are formed.

[0057] A plasma processing is conducted with helium gas having aconcentration of 700 seem at the pressure of 500 mTorr for 30 seconds.

[0058] An ashing process is conducted with oxygen plasma using abatch-type plasma ashing apparatus (OPM-EM 1000 manufactured by TokyoOhka Kogyo Co., Ltd.) at the pressure of 1000 mTorr for 300 seconds.

[0059]FIG. 1 shows the infrared absorption spectrum of the coating filmafter the ashing process. The peak showing Si—R (R is hydrogen atom) isapparent in FIG. 1, which indicates that there is no damage to thecoating film.

[0060] (Embodiment 2: Coating Liquid 2 and He Processing)

[0061] The same processing as in embodiment 1 is conducted, except thatcoating liquid 2 is used instead of coating liquid 1.

[0062]FIG. 2 shows the infrared absorption spectrum of the coating filmafter the ashing process. The peak showing Si—R (R is hydrogen atom) isapparent in FIG. 2, which indicates that there is no damage to thecoating film.

COMPARATIVE EXAMPLE 1 Coating Liquid 1 and no He Processing

[0063] The same processing as in embodiment 1 is conducted, except thata plasma processing with helium gas is not conducted.

[0064]FIG. 3 shows the infrared absorption spectrum of the coating filmafter the ashing process. The peak showing Si—R (R is hydrogen atom)slightly collapses in FIG. 3, which indicates that the coating film isdamaged.

COMPARATIVE EXAMPLE 2 Coating Liquid 2 and no He Processing

[0065] The same processing as in embodiment 2 is conducted, except thata plasma processing with helium gas is not conducted.

[0066]FIG. 4 shows the infrared absorption spectrum of the coating filmafter the ashing process. The peak showing Si—R (R is hydrogen atom)collapses in FIG. 4, which indicates that the coating film is damaged.

[0067] As is fully described in the above, according to the presentinvention, since an etching process is conducted to a silica groupcoating film having a dielectric constant equal to or less than 3.2formed on a substrate through a resist pattern, and thereafter, a plasmaprocessing is conducted to the silica group coating film with plasmainduced from inactive gas such as helium gas or the like, the silicagroup coating film is not damaged when an ashing process is conducted tothe resist pattern as a subsequent process, and the low dielectricconstant can be maintained.

[0068] Therefore, if the present invention is applied to the damascenemethod, it is possible to obtain a reliable semiconductor element.

[0069] Also, according to the present invention, since one kind selectedfrom polyalkylene glycol and the end alkylation product thereof isincluded in a coating liquid, the dielectric constant of the silicagroup coating film formed with the coating liquid can be lowered, whichis advantageous to micros.

[0070] Although there have been described what are the presentembodiments of the invention, it will be understood by persons skilledin the art that variations and modifications may be made thereto withoutdeparting from the gist, spirit or essence of the invention as set forthin the appended claims.

What is claimed is:
 1. A method for processing a coating film comprisingthe steps of: forming a silica group coating film, having a dielectricconstant equal to or less than 3.2 on a substrate; etching said silicagroup coating film through a resist pattern; processing said etchedsilica group coating film with plasma induced from a substantiallyinactive gas; and conducting an ashing process to said resist pattern.2. A method for processing a coating film as defined in claim 1, whereinsaid substantially inactive gas is helium gas.
 3. A method forprocessing a coating film as defined in claim 1, wherein a coatingliquid, for forming said silica group coating film in said film formingstep, comprises a condensation product which is obtained throughhydrolysis of trialkoxysilane within an organic solvent under an acidcatalysis.
 4. A method for processing a coating film as defined in claim3, wherein the coating liquid comprises at least one of polyalkyleneglycol and the end alkylation product thereof.
 5. A method formanufacturing a semiconductor element, comprising the steps of: (1)forming a silica group coating film, having a dielectric constant equalto or less than 3.2, on a substrate; (2) providing a resist pattern onsaid silica group coating film; (3) etching said silica group coatingfilm using said resist pattern as a mask; (4) processing said silicagroup coating film with plasma induced from a substantially inactivegas; and (5) conducting an ashing process to said resist pattern withplasma induced from oxygen gas.
 6. A method of manufacturing asemiconductor element as defined in claim 5, wherein said substantiallyinactive gas is helium gas.
 7. A method for manufacturing asemiconductor element as defined in claim 5, wherein said step offorming a silica group coating film involves formation of a silicondioxide film on said substrate using a coating liquid comprising acondensation product obtained through hydrolysis of a trialkoxysilane inan organic solvent under acid catalysis.
 8. A method for manufacturing asemiconductor element as defined in claim 5, wherein said step ofprocessing said silica group with plasma is conducted under a pressureof 10-600 m Torr for 30-300 seconds.
 9. A method for manufacturing asemiconductor element as defined in claim 5, wherein said step ofprocessing said silica group with plasma is conducted under a pressureof 100-500 m Torr for 30-120 seconds.